HAL Id: jpa-00230947
https://hal.archives-ouvertes.fr/jpa-00230947
Submitted on 1 Jan 1990
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
RECENT RESULTS AT INTERMEDIATE ENERGIES
C. Glashausser
To cite this version:
C. Glashausser. RECENT RESULTS AT INTERMEDIATE ENERGIES. Journal de Physique Col-
loques, 1990, 51 (C6), pp.C6-577-C6-582. �10.1051/jphyscol:1990677�. �jpa-00230947�
COLLOQUE DE PHYSIQUE
Colloque
C6,
supplementau
n022, Tome 51, 15 novembre 1990RECENT RESULTS A T INTERMEDIATE ENERGIES
C. G L A S H A U S S E R ( ~ )
D e p a r t m e n t of P h y s i c s , R u t g e r s U n i v e r s i t y , P i s c a t a w a y , NJ 08854, U . S . A .
RIsumh
-
Les p r e s e n t a t i o n s de S e s s i o n F s o n t d i s c u t e e s .A b s t r a c t
-
The papers p r e s e n t e d o r a l l y i n S e s s i o n F a r e d i s c u s s e d .B e f o r e commenting o n t h e i n t e r e s t i n g r e s u l t s p r e s e n t e d d u r i n g S e s s i o n F, l e t me say f i r s t t h a t f o u r of t h e seven t a l k s were p r e s e n t e d , and p r e s e n t e d v e r y w e l l , by g r a d u a t e s t u d e n t s . This i s a n o t h e r good reason f o r c o n t i n u i n g n e x t time t h e p o l i c y i n t r o d u c e d h e r e of p r o v i d i n g a t l e a s t p a r t i a l s u p p o r t f o r s t u d e n t t r a v e l and r e g i s t r a t i o n .
We b e g a n o u r s e s s i o n w i t h p i o n s , two of t h e few experiments w i t h p i o n s t h a t we have h e a r d a b o u t a t t h i s m e e t i n g . Now t h a t p o l a r i z e d n u c l e a r t a r g e t s a r e becoming more a v a i l a b l e , it i s l i k e l y t h a t we w i l l s e e a l o t more pion-nucleus a n a l y z i n g power d a t a i n t h e next few y e a r s . J. GBrgen ( o n e o f o u r s t u d e n t s ) t o l d u s a b o u t t h e f i r s t d a t a o n a s y m m e t r i e s i n t h e p i o n s i n g l e - c h a r g e exchange r e a c t i o n on a n u c l e u s , h e r e p o l a r i z e d 13c.
The u l t i m a t e aim, a s i n s t u d i e s of pion s c a t t e r i n g on p o l a r i z e d t a r g e t s , is t o l e a r n more a b o u t t h e l i t t l e - k n o w n p i o n - n u c l e u s s p i n - f l i p amplitude g ( @ ) i n n u c l e i . Along t h e way, some i n t e r e s t i n g s t r u c t u r e and r e a c t i o n q u e s t i o n s w i l l have t o b e addressed, a s t h e f i r s t t h e o r e t i c a l c a l c u l a t i o n s s u g g e s t . The d a t a , w i t h p i o n s of 163 MeV from LAMPF, f o r two r e s o l v e d s t a t e s a r e shown i n Fig. 1 along w i t h very r e c e n t p r e d i c t i o n s by S i e g e l and by C h a k r a v a r t i ; t h e t w o c a l c u l a t i o n s , a s I u n d e r s t a n d them, a r e b a s i c a l l y i m p u l s e approximation c a l c u l a t i o n s w i t h t h e same n u c l e a r wave f u n c t i o n s , b u t d i f f e r e n t i n g r e d i e n t s t o d e s c r i b e t h e r e a c t i o n . N e i t h e r does v e r y w e l l o v e r a l l , b u t t h e curve of S i e g e l does d e s c r i b e a t l e a s t t h e low q d a t a f o r t h e g r o u n d s t a t e . The v a l u e s o f AV a r e l a r g e , a v i r t u e I t h i n k , and very d i f f e r e n t f o r t h e two s t a t e s . I n c o n t r a s t , t h e a n a l y z i n g powers f o r e l a s t i c p i o n s c a t t e r i n g on
13c,
shown by Y, Yen, a r e g e n e r a l l y q u i t e s m a l l ; an example i s i l l u s t r a t e d i n Fig. 2.' Her r e s u l t s a t 231 MeV a r e even s m a l l e r . Such s m a l l v a l u e s of A have a l s o been s e e n i n t h e o n l y previous d a t a a v a i l a b l e ( s e e C o n t r i b u t i o n 7 F ) . Herev
t h e n u c l e a r s t r u c t u r e dependence can b e s e e n i n t h e comparison of t h e two c a l c u l a t i o n s by Mach; t h e wave f u n c t i o n s a r e t h o s e o f Cohen and K u r a t h o r T i a t o r . The r e s u l t s f o r A+
s c a t t e r i n g w i t h t h e T i a t o r wave f u n c t i o n s a r e q u i t e good, though t h e same wave f u n c t i o n s f a i l t o y i e l d a good d e s c r i p t i o n f o r II- s c a t t e r i n g where t h e e x t r a n e u t r o n i n
13c
i s much more important. While it i s t o o e a r l y t o make a r e l i a b l e f o r e c a s t-
t h e d a t a t h u s f a r a r e few, and t h e c a l c u l a t i o n s q u i t e p r e l i m i n a r y-
t o me it appears t h a t i t w i l l b e some t i m e b e f o r e c l e a r i n f o r m a t i o n about g ( 6 ) can be e x t r a c t e d from such r e s u l t s .P r o f e s s o r A r a i brought quarks e x p l i c i t l y i n t o our s e s s i o n , w i t h r e s u l t s from KEK on t h e p o l a r i z a t i o n o f lambdas produced i n t h e
n +
"C r e a c t i o n a t 4 GeV/c. Here t h e i d e a was t o i n v e s t i g a t e e f f e c t s of t h e n u c l e a r many-body system on quark p r o d u c t i o n by l o o k i n g a t backward a n g l e s w h e r e q u a s i e l a s t i c p r o d u c t i o n o f lambdas o n a s i n g l e n u c l e o n i s s t r o n g l y reduced. The p o l a r i z a t i o n r e s u l t s a r e shown by t h e d a r k c i r c l e s i n F i g . 3. We l e a r n e d from H e l l e r y e s t e r d a y t h a t P* is g e n e r a l l y n e g a t i v e a t h i g h e n e r g i e s and forward a n g l e s ; h e r e it i s p o s i t i v e . An a t t e m p t t o d e s c r i b e t h e s e d a t a w i t h a model b a s e d on i n c o h e r e n t p r o d u c t i o n on nucleons i n a Fermi g a s , i . e . , a model w i t h o u t many-body e f f e c t s , f a i l s completely a s s e e n by t h e curves i n t h e lower h a l f of t h e f i g u r e . The s o l i d c u r v e i s b a s e d o n t h e s o - c a l l e d c o h e r e n t t u b e model and o n p r e c e s s i o n i n t h e c o l o r f i e l d d e s c r i b e d by H e l l e r . This curve . i s reasonably c l o s e t o t h e d a t a . The a u t h o r s t a k e t h i s a s e v i d e n c e f o r a n u c l e a r many body e f f e c t a t t h e q u a r k l e v e l-
j u s t what t h e y were looking f o r . T h i s , of c o u r s e , w i l l be v e r y i n t e r e s t i n g i f it can be confirmed. C l e a r (-0 Supported i n p a r t by t h e N a t i o n a l Science Foundation.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990677
COLLOQUE DE PHYSIQUE
Q,, ( deg. 1
F i g . 1
-
Analyzing powers measured i n t h e 132(lr+,fl) N ground s t a t e r e a c t i o n a t 13 163 MeV.The t h e o r e t i c a l c a l c u l a t i o n s a r e by S i e g e 1 ( s o l i d ) and C h a k r a v a r t i (dashed).
' 3 c ( ~ + , ~ c ) 1 3 ~
TT = 132 MeV
-
-
-
1 1 1 1 1
Fig. 2
-
Analyzing powers measured f o r i n e l a s t i c p i o n s c a t t e r i n g from 13c a t 132 MeV. The t h e o r e t i c a l c a l c u l a t i o n s by Mach u s e d Cohen-Kurath ( s o l i d ) o r T i a t o r ( d a s h e d ) wave f u n c t i o n s .evidence of a dependence on t h e t a r g e t mass A
-
a dependence n o t s e e n i n H e l l e r s d a t a-
would b e a f i r s t s t e p . Such a program i s beginning a t KEK.
On Tuesday, O t t o HXusser mentioned t h a t a r e d u c t i o n i n t h e v a l u e s o f A m e a s u r e d a t Y
t h e q u a s i e l a s t i c peak f o r i n c l u s i v e p r o t o n i n e l a s t i c s c a t t e r i n g can be e x p l a i n e d by Dirac- based models and n o t , n o t y e t a t l e a s t , by n o n - r e l a t i v i s t i c c a l c u l a t i o n s . The e f f e c t i s a t t r i b u t e d t o t h e c h a n g e i n t h e e f f e c t i v e mass of t h e nucleon i n s i d e t h e nucleus due t o t h e l a r g e s c a l a r and v e c t o r p o t e n t i a l s . Andy M i l l e r d e s c r i b e d t o u s e x c l u s i v e ( p , 2 p )
+
e x p e r i m e n t s a t 500 MeV a t TRIUMF, where he looked f o r e x p l i c i t evidence of t h e d e n s i t y - d e p e n d e n c e i n h e r e n t i n s u c h a n e x p l a n a t i o n by c o m p a r i n g A f o r s s t a t e and p s t a t e
Y
k n o c k o u t f r o m 160. The S s t a t e r e s u l t s , i n Fig. 4, r e v e a l very l a r g e r e d u c t i o n s i n A Y from t h e f r e e v a l u e s shown by t h e dashed curves. The r e d u c t i o n s s e e n f o r p - s t a t e knockout
F i g . 3
-
P o l a r i z a t i o n o f lambdas measured i n i n c l u s i v e p r o d u c t i o n w i t h 4 GeV/c pions on12c
( s o l i d c i r c l e s ) . Previous d a t a a r e shown by t h e X ' S . The t h e o r e t i c a l c u r v e s a r e d e s c r i b e d i n t h e t e x t .I l 1 I
(20' .
55'). - . _ _ . _ . _ . _ - . . - -
m
DWlA -
DD-DWIA -
-
1 , ? 1
-
f
l I 1 I
Fig. 4
-
Analyring powers measured i n t h e 160 (;,2p) 1 5 ~ r e a c t i o n w i t h s I l 2 knockout. The>
-0.2d o t t e d c u r v e s a r e impulse approximation c a l c u l a t i o n s ; t h e s o l i d c u r v e s have a r e l a t i v i s t i c change i n t h e e f f e c t i v e mass of t h e nucleon included.
-0.2
1
170 210 250 290330 370
120 160 200 240 280 3204 z
4 T
LEFT - T
RIGHT ( MeV)
C6-580 COLLOQUE DE PHYSIQUE
w e r e i n d e e d s i g n i f i c a n t l y s m a l l e r , a s expected s i n c e p - s t a t e wavefunctions sample l e s s of t h e i n t e r i o r o f t h e n u c l e u s . An a t t e m p t t o d e s c r i b e t h e s e d a t a b y i n s e r t i n g a r e l a t i v i s t i c d e n s i t y - d e p e n d e n c e (DD) i n t o a DWIA c o d e was r e a s o n a b l y s u c c e s s f u l . A complete r e l a t i v i s t i c c a l c u l a t i o n of t h e (;,2p) r e a c t i o n i s e x p e c t e d s o o n . I n o r d e r t o t e s t whether t h i s r e d u c t i o n i n A is r e a l l y a s i g n a t u r e of r e l a t i v i s t i c e f f e c t s i n n u c l e i ,
Y
-t
i t is important t o c a r r y o u t e q u a l l y complete n o n - r e l a t i v i s t i c c a l c u l a t i o n s of ( p , 2 p ) . A s t r o n g e f f o r t i n t h i s d i r e c t i o n was d e s c r i b e d by H. A r e l l a n o , t h e o n l y t h e o r i s t on our program. The nucleons i n t h g nucleus o b v i o u s l y move, b u t most s c a t t e r i n g c a l c u l a t i o n s don't t a k e t h i s motion i n t o account p r o p e r l y . We have heard about t h e importance of Fermi motion i n t h e p l e n a r y s e s s i o n t a l k s of Hausser and Baker. The c a l c u l a t i o n of A r e l l a n o e t a l . i s a f u l l - f o l d i n g c a l c u l a t i o n f o r e l a s t i c s c a t t e r i n g , a f u l l - i n t e g r a t i o n over t h e momentum-space wave f u n c t i o n o f t h e c o n t r i b u t i n g o r b i t a l s w i t h a n o f f - s h e l l t m a t r i x d e p e n d e n t o n momentum and energy embedded in-between. The r e s u l t s a t 200 MeV f o r p r o t o n e l a s t i c s c a t t e r i n g from 4 0 ~ a a r e p l o t t e d i n F i g . 5. The f u l l - f o l d i n g (FF) c a l c u l a t i o n i s shown on t h e l e f t , t h e s t a n d a r d t p approximation c a l c u l a t i o n on t h e r i g h t . The dashed and s o l i d l i n e s compare r e s u l t s based on t h e P a r i s and Bonn p o t e n t i a l s , r e s p e c t i v e l y . With b o t h p o t e n t i a l s , t h e e f f e c t s o f f u l l - f o l d i n g o n A a r e v e r y l a r g e , and r e m i n i s c e n t of
Y
r e s u l t s observed i f a s t a n d a r d t p c a l c u l a t i o n i s based on t h e D i r a c e q u a t i o n i n s t e a d o f t h e S c h r o d i n g e r e q u a t i o n . A r e a l comparison w i t h d a t a should await t h e i n c l u s i o n of t h e d e n s i t y - d e p e n d e n c e a r i s i n g f r o m t h e P a u l i P r i n c i p l e i n t h e s e n o n - r e l a t i v i s t i c c a l c u l a t i o n s . The n e x t s t e p
-
t h e one I would p a r t i c u l a r l y l i k e t o s e e happen soon-
is t o extend t h e s e c a l c u l a t i o n s t o i n e l a s t i c s c a t t e r i n g and t h e (p,2p) r e a c t i o n .F i g . 5
-
F u l l - f o l d i n g ( F F ) and s t a n d a r d ( t p ) c a l c u l a t i o n s f o r 200 MeV p r o t o n e l a s t i c s c a t t e r i n g from 4 0 ~ a . The s o l i d c u r v e s a r e based on t h e Bonn p o t e n t i a l , t h e dashed curves on t h e P a r i s p o t e n t i a l .Saturne I1 is the only facility where intermediate energy polarized deuterons are available, and polarized deuterons provide the only direct means of seeing the T=O, S=l response of nuclei. Polarization-transfer measurements are the way to separate the S=O and S=l responses in (p,p' )
,
as we have seen on Tuesday. Measurements with deuterons generally require both vector and tensor polarization measurements, but n o tensor polarimeter has yet been built to cover a wide range of energies in the focal plane at energies of 400 MeV or more. M. Morlet presented results from vector polarization transfer measurements for separated S=O and S=l states in 12c at 400 MeV which indicate that tensor polarization measurements may not be necessary, at least for an initial survey of T=O, S=l strength. Fig. 6 shows a quantity labelled, : E
the proposed signature of S=1 strength, for known S=O and S=l states at several angles. This: E
is a combination of observables which is like the spin-flip probability for deuterons. The results in Fig. 6 show a clear distinction between S=O and S=l states, and thus a nice signature of S=l excitation. In order to use this signature for a quantitative extraction of S=l strength in the continuum, good microscopic calculations of the (d, d' ) reaction are necessary.This conference has provided a convenient avenue for encouraging theorists to move in this direction.
We closed our session with a review by Alena Opper of several new measurements of spin-transfer observables for isolated states in (p,p7) carried out at Indiana around 200 MeV. Here the goal is the determination of the effective NN interaction inside nuclei (and understanding it in terms of Pauli corrections, changes in the effective masses of mesons in nuclei, etc.). Ed Stephenson told us on Tuesday about evidence of such medium effects for S=l, T=l excitations at high momentum transfer. Fig. 7 shows the present state of affairs for a T=O state, the 19.80 MeV 4 - state in 160. The DK shown here
..
correspond to the four different spin-dependent components of the NN interaction; each is a combination of spin-transfer observables which, in the PWIA, is proportional to a single component. The curves illustrated correspond to non-relativistic DWIA calculations with the Bonn interaction, including Pauli corrections. These give a reasonable but not perfect account of these and several other T=O data, and thus indicate only small, if any,exotic medium corrections in this channel. In order to determine whether the NN interaction in nuclei really is different from the free space interaction in interesting ways, it is important to carry out precise measurements of this sort for several well known states, e.g., stretched states, over a range of energies. This is only now beginning.
Fig. 6
-
The signature: E
of S=1 transitions determined from the 12~(d,d7) reaction. The data for the S=l l+ 12.71 MeV state are shown by the solid circles. Data for three S=O states are combined into the vertical lines with negative values.COLLOQUE DE PHYSIQUE
F i g . 7
-
Measured values of the D parameters f o r the 1 9 . 8 0 MeV 4 - T=O s t a t e i n 160 with K200 MeV protons. The s o l i d curves are n o n - r e l a t i v i s t i c DWIA c a l c u l a t i o n s based on t h e Bonn p o t e n t i a l .
